Influence of magnesium on physiological responses of wheat infected by Pyricularia oryzae

Abstract

Although magnesium (Mg) is considered an essential element for wheat growth, its importance for disease control has often been overlooked, and the physiological features of diseased plants mediated by Mg remain elusive. In this study, the effect of three Mg concentrations (0·25, 2·5 and 4 mm) on wheat resistance to leaf blast (Pyricularia oryzae), leaf gas exchange, invertase activity, cellular damage and foliar concentration of photosynthetic pigments and nutrients was investigated. Foliar Mg increased from 1·9 to 3·9 g kg-1, whereas calcium (Ca) decreased from 7·8 to 4·9 g kg-1 as the applied Mg increased from 0·25 to 4 mm. Blast severity increased from 11·3 to 39·6% as the applied Mg increased from 0·25 to 4 mm. Photosynthesis, stomatal conductance, transpiration and photosynthetic pigment concentrations decreased in inoculated plants compared to non-inoculated plants regardless of the Mg concentration; however, the reductions were more pronounced for plants grown with 4 mm Mg than those grown with 0·25 mm Mg. On the other hand, a higher internal CO2 concentration, invertase activity and malondialdehyde concentration was recorded in inoculated plants grown with 4 mm Mg compared to those grown with 0·25 mm Mg. In conclusion, reduced Ca uptake may partially explain the increased susceptibility of wheat to leaf blast with the highest Mg concentration. Mg-induced susceptibility to leaf blast appeared responsible for the photosynthetic impairments. These were most probably due to biochemical constraints because plants grown with the highest Mg concentration suffered extensive cellular damage and degradation of photosynthetic pigments as a result of high disease severity.